DynamicWorkerLoader

Source: src/Cloudflare/Workers/DynamicWorkerLoader.ts

Load and run ephemeral Workers at runtime from inline JavaScript modules.

DynamicWorkerLoader registers a worker_loader binding on the parent Worker at deploy time. At runtime you call .load() with inline module source code and get back a fully typed Worker instance you can fetch or call RPC methods on. Each loaded Worker runs in its own isolate with full sandboxing.

This is useful for evaluating user-provided code, running untrusted plugins, or dynamically generating Workers from templates.

Creating a Loader

Yield Cloudflare.DynamicWorkerLoader in your Worker’s init phase to register the binding. The string argument becomes the binding name on the deployed Worker.

// init
const loader = yield* Cloudflare.DynamicWorkerLoader("Loader");

Loading a Worker

Call loader.load() with a compatibility date, a main module name, and a map of module names to source code strings. The returned instance exposes .fetch() for HTTP and RPC methods for named entrypoints.

const worker = loader.load({
  compatibilityDate: "2026-01-28",
  mainModule: "worker.js",
  modules: {
    "worker.js": `export default {
      async fetch(request) {
        return new Response("Hello from dynamic worker!");
      }
    }`,
  },
});

const response = yield* worker.fetch(
  HttpClientRequest.get("https://worker/"),
);

Sandboxing

Set globalOutbound to null to block all outbound network access from the dynamic Worker, or pass an RPC stub to intercept and proxy outbound requests.

const worker = loader.load({
  compatibilityDate: "2026-01-28",
  mainModule: "worker.js",
  modules: {
    "worker.js": `export default {
      async fetch(req) {
        // fetch() calls from here will fail
        return new Response("sandboxed");
      }
    }`,
  },
  globalOutbound: null,
});

Named Entrypoints

If the dynamic Worker exports named entrypoints, use .getEntrypoint(name) to get a typed stub for calling its methods.

const worker = loader.load({ ... });
const api = worker.getEntrypoint<{ greet: (name: string) => Effect.Effect<string> }>("api");
const greeting = yield* api.greet("world");